Method for strengthening a brittle oxide substrate, silane-based compositions, and a polymerized cross-linked siloxane coated brittle oxide substrate

ABSTRACT

A method is described for strengthening or restoring strength to a brittle oxide substrate which includes the steps of coating the brittle oxide substrate with an aqueous solution containing a silane-based composition, and curing the coating to form a transparent layer on the brittle oxide substrate. Also disclosed are novel compositions used to coat brittle oxide substrates, and silane-coated brittle oxide containers.

This application is a division of application Ser. No. 08/344,621, filedNov. 17, 1994, pending; which is a continuation of application Ser. No.08/078,811, filed Jun. 21, 1993, abandoned; which is acontinuation-in-part of application Ser. No. 08/043,980, filed Apr. 7,1993, abandoned; which is a continuation of application Ser. No.07/873,315, filed Apr. 24, 1992, abandoned; which is acontinuation-in-part of application serial No. 07/575,052, filed Aug.30, 1990, abandoned. This application is also a continuation-in-part ofU.S. Ser. No. 07/986,894, filed Dec. 8, 1992, abandoned; which is acontinuation application serial No. 07/738,030, filed Jul. 30, 1991,abandoned; which was a division of application serial No. 07/575,052,filed Aug. 30, 1990, abandoned, the contents of which are relied uponand incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a method of strengthening a brittleoxide substrate and also relates to aqueous solutions containingsilane-based compositions and polymerized cross-linked siloxane coatedbrittle oxide substrates. More particularly, the present inventionrelates to a method of strengthening or restoring strength to a glasscontainer and the resulting polymerized cross-linked siloxane coatedglass container.

Brittle materials, such as glass substrates, generally exhibit somemechanical properties, such as, e.g., tensile strength, which aresubstantially lower than predicted. This manifestation can arise as theresult of such factors as imperfections in the structure of a testspecimen, or small amounts of impurities in either the body or thesurface of an article made of that material. Progressive zone melting toreform the crystalline structure and floating impurities out of themelted brittle material have been used in the past for brittle metals inan attempt to improve the mechanical properties of the brittle metals.Also, with regard to non-metal brittle materials, multi-layer structuresmade of the brittle material have been used to improve mechanicalproperties. In addition, surface treatments of the brittle material havebeen used to protect the surface from abrasion and to provide a smallmeasure of support to brittle articles.

Glass is intrinsically one of the strongest materials known to man.Theoretically, standard silicate glasses should be able to supportstresses as high as 14 to 20 gigapascals (2 to 3 million pounds persquare inch (psi)). In practice, however, the strengths typicallyobtained are on the order of 70 megapascals (MPa), about 10,000 psi.

The explanation of the discrepancy between predicted and measured valuesis the existence of surface flaws or cracks. These flaws essentiallyfracture the siloxane network (Si--O--Si), which is the backbone of theglass. This damage to the glass acts to concentrate any applied force tothe point of causing catastrophic failure of the glass article,typically at much lower stresses than otherwise expected. Whiledescribed here for glass, this same theory can be applied to any brittlematerial not demonstrating significant plastic deformation prior tofailure.

In the case of a glass container, for example, the surface flaws ordefects can originate from many sources, ranging from unmelted batchmaterials to scratches produced by sliding across hard surfaces,including other glass articles. In a typical container-manufacturingfacility for example, the glass articles can be heavily damaged byhandling from the moment they are formed. Contact with particulates andmoisture in the air, other bottles, guiderails and other handlingequipment, and the conveyor on which they are transported, can lead tolarge decreases in the strength of the container due to the flawsproduced.

Researchers have long sought a means to alleviate the problems withglass strength. Many modifications to the forming and handling processhave led to unsatisfactory increases in the strength because thesemodifications in handling still leave flaws in the surface. For thisreason, it has been a goal of researchers to reduce the effect of flawsafter they are inevitably formed on the object.

Some approaches to improving the strength of glass include Aratani etal., U.S. Pat. No. 4,859,636, wherein metal ions in the glass areexchanged with ions of a larger radius to develop a surface compressivestress. Poole et al., U.S. Pat. No. 3,743,491, also relates to a surfacecompressive stress, but provides a polymer overcoat to protect thesurface from further abrasion. Hashimoto et al., U.S. Pat. No.4,891,241, relates to treating the surface of the glass with a silanecoupling agent followed by a polymer coating containing acryloyl and/ormethacryloyl groups, followed by irradiation or thermal treatment topolymerize the molecules containing those groups. The '241 patentfurther shows that silanes alone do not strengthen substrates and thatacrylates are necessary for any strengthening.

While the patents described above each provide some improvement to thestrength of the glass so treated, they are not without shortcomings.Some of these treatments require longer times than available duringmanufacturing, necessitating off-line processing. There are alsoconcerns related to worker safety and health. In particular, the use andhandling of organic solvents, as well as the acrylate and methacrylatecompounds, are a safety and health concern to the manufacturer.

Therefore, there is an unmet need for a method of strengthening abrittle oxide substrate which addresses the above concerns as well asprovides acceptable increases in strength to the brittle oxidesubstrate. There is also a need for a coated brittle oxide substratewhich has a substantially improved strength when compared to a brittleoxide substrate without any coating.

Further, there is a need for a method of strengthening a brittle oxidesubstrate which will also provide acceptable labelability and/orhumidity resistance.

In addition, there is a need for a polymerized cross-linked siloxanecoated brittle oxide substrate wherein the cured coating is transparent.

Additional objects and advantages of the present invention will be setforth in part in the description which follows, and in part will beobvious from the description, or may be learned by practice of thepresent invention. The objects and advantages of the present inventionwill be realized and attained by means of the elements and combinationsparticularly pointed out in the appended claims.

BRIEF SUMMARY OF THE PRESENT INVENTION

To achieve the objects and in accordance with the purposes of thepresent invention, as embodied and broadly described herein, the presentinvention relates to a method of strengthening a brittle oxide substratewhich includes the following steps. First, the brittle oxide substrateis coated with an aqueous solution containing a silane-basedcomposition. The aqueous solution containing the silane-basedcomposition is substantially absent of any organic solvent. Further, thesilane-based composition upon being hydrolyzed in the aqueous solutionhas the following formula:

    (OH).sub.3 SiR"

with R" being an organofunctional group. After coating the aqueoussolution containing the hydrolyzed silane-based composition onto thebrittle oxide substrate, the coating is cured to form a transparentlayer on the brittle oxide substrate. Also, R" in the silane-basedcomposition is selected so that (i) the strength of the brittle oxidesubstrate having the cured coating is substantially improved compared tothe strength of the brittle oxide substrate prior to the coating stepand (ii) the cured coating does not interfere with the labelability ofthe brittle oxide substrate.

The present invention also relates to a method similar to the onedescribed above, except R" is selected so that (i) the strength of thebrittle oxide substrate having the cured coating is substantiallyimproved compared to the strength of the brittle oxide substrate priorto the coating step and (ii) the substantially improved strength fromthe cured coating on the brittle oxide substrate has a maintainedhumidity resistance of at least about 50%.

Also, the present invention relates to a polymerized cross-linkedsiloxane coated brittle oxide container. In particular, the polymerizedcross-linked siloxane coated brittle oxide container includes a brittleoxide container and a transparent layer of polymerized cross-linkedsiloxane preferably cured onto the outer surface of the brittle oxidecontainer. The polymerized cross-linked siloxane is formed from asilane-based composition hydrolyzed in an aqueous solution andsubstantially lacks the presence of an organic solvent. The hydrolyzedsilane-based composition, for example, can be selected from the groupconsisting of methacryloxypropyltrimethoxysilane (MPTMO),glycidoxypropyltrimethoxysilane (GPTMO), vinyltrimethoxysilane (VTMO),2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane (CETMO),methyltrimethoxysilane (MTMO), 3,3-dimethoxypropyltrimethoxysilane(DMPTMO), 5,6-epoxyhexyltrimethoxysilane (EHTMO)N-(trimethoxysilylpropyl)-maleic acid amide,3-ureidopropyltrimethoxysilane (UPTMO), 1,2-bis(trimethoxysilyl)ethane(BTMOE), 1,2-bis(3-trimethoxysilylpropoxy)ethane (BTMOPE), hydrolyzedforms thereof and mixtures thereof.

The present invention further relates to novel silane-based compositionsincluding, but not limited to, a mixture of vinyltrimethoxysilane and2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane; a mixture ofmethyltrimethoxysilane and 2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane;a mixture of glycidoxypropyltrimethoxysilane, 2-(3,4epoxycyclohexyl)ethyltrimethoxysilane, and methyltrimethoxysilane; and amixture of glycidoxypropyltrimethoxysilane and 2-(3,4epoxycyclohexyl)ethyltrimethoxysilane.

The above generally described invention overcomes the difficultiesencountered in working with brittle oxide substrates such as glass. Themethod of the present invention drastically and unexpectedly increasesor restores the strength of brittle oxide substrates as compared to thestrength of the substrate prior to receiving any coating. Further, thecoatings of the present invention are transparent and safe to use onbrittle oxide substrates. Besides increasing or restoring the strengthof the substrate, the coatings of the present invention preferably donot interfere with labelability which has been a problem in the pastwith coatings on substrates.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the present invention, as claimed.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The brittle oxide substrate used in the method of the present inventioncan be made of any brittle oxide material such as aluminum oxides oraluminates, silicon oxides or silicates, titanium oxides or titanates,germanates, or glass made from, for instance, the above materials.Further, the brittle oxide substrate can be of any form such as a glassbottle.

The silane-based compositions upon being hydrolyzed in the aqueoussolution have the following formula:

    (OH).sub.3 SiR"

wherein R" is an organofunctional group which may or may not hydrolyzein the aqueous solution. This organofuctional group may include residuesof hydrolyzable silanes. The selection of R" is further based on therequirement that the resulting aqueous solution containing thehydrolyzed silane-based composition after being coated and cured on thebrittle oxide substrate imparts a substantially improved strength to thebrittle oxide substrate and does not interfere with the labelability ofthe brittle oxide substrate.

Preferred examples of R" include glycidoxypropyl, 2-(3,4epoxycyclohexyl)ethyl, 3,3-dimethoxypropyl, 3-ureidopropyl, andhydrolyzed forms thereof.

Accordingly, preferred examples of the hydrolyzed silane-basedcompositions include hydrolyzed glycidoxypropyltrimethoxysilane,hydrolyzed 2-(3,4 epoxycyclohexyl)ethyltrimethoxysilane, hydrolyzed3-ureidopropyltrimethoxysilane, and hydrolyzed3,3-dimethoxypropyltrimethoxysilane.

The coating applied to the brittle oxide substrate can also be a mixtureof one or more hydrolyzed silane-based compositions. The mixture of twoor more hydrolyzed silane-based compositions is especially advantageouswhen it is known that one hydrolyzed silane-based composition providesexcellent labelability and another hydrolyzed silane-based compositionprovides excellent strength enhancing properties. Thus, a mixture wouldprovide the desired balance of properties, that is, a coating whichprovides improved strength and which does not interfere withlabelability. For instance, a mixture of hydrolyzed CETMO andmethyltrimethoxysilane (MTMO) can be used to obtain this balance ofproperties.

Other examples of hydrolyzed silane-based compositions which can be usedin mixtures of one or more hydrolyzed silane-based compositions includehydrolyzed methacryloxypropyltrimethoxysilane, hydrolyzed3-ureidopropyltrimethoxysilane, hydrolyzed1-2-bis(trimethoxysilyl)ethane, hydrolyzed1,2-bis(3-trimethoxysilylpropoxy)ethane, hydrolyzed5,6-epoxyhexyltrimethoxysilane, hydrolyzedN-(trimethoxysilylpropyl)-maleic acid amide, hydrolyzeddimethyltetramethoxydisiloxane, and hydrolyzedN-(3-triethoxysilylpropyl)4-hydroxybutyramide (HBTEO). Thesecompositions, for instance, can be used in a mixture with hydrolyzedCETMO and/or hydrolyzed GPTMO and/or hydrolyzed DMPTMO. Generally, thesilane-based compositions used in a mixture can be added in equalproportions. Of course, if stronger labelability properties are desired,a greater proportion of hydrolyzed CETMO, hydrolyzed GPTMO, orhydrolyzed DPTMO, for instance, would be added. Further, any of thecompositions described herein can be used alone to substantially improvethe strength of a brittle oxide substrate, if labelability is not aconcern.

Unless stated otherwise, the silane-based compositions provided asspecific examples are commercially available from one or more of thefollowing sources, Union Carbide, Dow Corning, Huls America and PCR,Inc.

While the coatings of the present invention can be mixtures of one ormore hydrolyzed silane-based compositions, separate coatings ofhydrolyzed silane-based compositions can be applied to a surface of abrittle oxide substrate. For example, a coating of CETMO can be appliedto a surface of a brittle oxide substrate and then while the CETMOcoating is still wet or dry or after curing the first coating, a secondcoating, another CETMO coating or a different coating (e.g. MPTMO), canbe applied.

Any number of such consecutive separate coatings can be applied in thismanner. Further, a surfactant can be applied in this manner, namely,coating a brittle oxide surface with a surfactant before and/or aftercoating the surface with a hydrolyzed silane-based composition(s). Evencoatings like that of Hashimoto et al. (U.S. Pat. No. 4,891,241) can beapplied after applying the coatings of the present invention.

It is to be understood that by applying the coating(s) of the presentinvention to a surface of a brittle oxide substrate, this also includesapplying the coating(s) of the present invention to any previous coatingon the brittle oxide substrate. An example of a previous coating wouldinclude hot-end coatings, typically applied in the industry.

The silane-based compositions used in the method of the presentinvention can be present in the aqueous solution at an averageconcentration from about 1% to about 99% by weight in water or aqueoussolution, preferably from about 1% to about 30% and most preferably fromabout 2% to about 10%.

With regard to the aqueous solution containing a hydrolyzed silane-basedcomposition, the amount of water added to the silane-based compositionto prepare the aqueous solution of the present invention is based on theconcentration of the resulting aqueous solution desired. A more dilutehydrolyzed silane-based composition would simply mean that more aqueoussolution containing the hydrolyzed silane-based composition would needto be coated onto the brittle oxide substrate to achieve thesubstantially improved strength in the brittle oxide substrate.

As used herein, the term "solution" includes chemical solutions,suspensions, emulsions, and mixtures, any of which may exhibit completeor incomplete intermixing.

The aqueous solution containing the hydrolyzed silane-based compositioncan be prepared all at once, meaning the silane-based composition isadded to water at the manufacturing facility. Alternatively, thehydrolyzed silane-based composition can be prepared as a neat orconcentrate and, at the user site, can be diluted with water in order toprepare the aqueous solution containing the hydrolyzed silane-basedcomposition for actual coating onto the brittle oxide substrate.

Further, the aqueous solution containing the hydrolyzed silane-basedcomposition of the present invention is substantially free of an organicsolvent, meaning no organic solvent is intentionally added to thesolution. Some organic compounds, however, may be present as an impurityand/or by-product of the silane-based composition reacting with water orthe aqueous solution reacting upon curing. Further, some of thecommercially available silane-based compounds may contain organicsolvents which are diluted upon being introduced into the aqueoussolution so that the percent solvent is approximately equal to or lessthan the silane concentration in the aqueous solution. One example isUPTMO.

Of course, it is known that the addition of a solvent can increase thestability of a solution.

The following reaction scheme sets forth the two reactions which arebelieved to occur in the preparation and application of the aqueoussolution containing the hydrolyzed silane-based composition.

    (R'O).sub.3 SiR+3H.sub.2 O⃡(OH).sub.3 SiR"+3R'OH→Si--O--Si coating

In this reaction, the trialkoxy silane reacts in water to form thetrisilanol in solution. The trisilanol in solution can containoligomers. Then, the trisilanol in solution condenses to form thepolymerized cross-linked siloxane (Si--O--Si) coating upon curing. Thissiloxane (Si--O--Si) coating generally contains an organicsubstituent(s) such as the R" group (s).

In this reaction scheme, R'O can be any group that is hydrolyzable. Thefollowing R' groups best meet this criteria, --CH₃, --C₂ H₅, and##STR1##

However, other groups which meet this criteria are well known to thoseskilled in the art.

The R group is an organofunctional group that may hydrolyze during thehydrolysis reaction to form the R" group. This organofunctional groupcan be a residue of a hydrolyzable silane. Following the hydrolysisreaction and if the R group is hydrolyzable, the R" group contains atleast one hydroxyl (OH) group. If the R group is not hydrolyzable, thenR and R" would be the same, for instance, when R is vinyl or methyl. Ingeneral, the R group in the above reaction scheme is preferably selectedso that the silane-based compositions of the present invention providethe appropriate balance between improved or restored strength andlabelability. Accordingly, preferred examples of the R group includeglycidoxypropyl, 2-(3,4 epoxycyclohexyl)ethyl, and 3,3-dimethoxypropyl.Further, preferred examples of the R" group would be hydrolyzed versionsof these preferred R compounds.

The above-described reaction scheme by no means is meant to limit themanner in which the aqueous solution containing the silane-basedcomposition is prepared. Instead of starting with trialkoxy silanes, onecan just as easily begin with any hydrolyzable silane. For instance,halide silanes such as substituted trichlorosilanes.

As noted above, upon hydrolysis, the R group can become hydroxyl (OH)containing as the R" group. For example, CETMO and GPTMO which both havean epoxy ring in the R group, upon hydrolysis in the aqueous solution,will result in a dihydroxy group by the opening of the epoxide ringwhile the rest of the R" group remains hydrophobic. Thus, the R" grouphas a balance of hydrophilic (provided by the OH groups) and hydrophobicproperties. The hydrophilic properties in the R" group particularlyimprove the strength and the labelability.

A surfactant can be added to the aqueous solution containing thehydrolyzed silane-based composition to improve coverage of the aqueoussolution containing the hydrolyzed silane-based composition around thebrittle oxide substrate surface which results in a greater strengtheningof the brittle oxide substrate and better appearance. Generally, only asmall amount of surfactant is added to allow the silane coating tospread out better on the brittle oxide substrate. Non-ionic surfactantshave been especially useful in this regard. One example of such asurfactant is commercially available Triton X-102 (obtained from UnionCarbide) which is octylphenoxy polyethoxy ethanol. Generally, from about0.001 wt. % to about 1.0 wt. % (based on total weight of solution) of asurfactant can be added. Preferably, from about 0.01 wt. % to about 0.05wt. % (based on total weight of solution) of a surfactant is added.

Those skilled in the art will realize that other compounds, pounds (e.g,a lubricant) can be added to the aqueous solution containing thesilane-based composition for the purpose of improving the wetting, orproviding other effects such as U.V. stability or control of rheologicalproperties.

The pH of the aqueous solution containing the silane-based compositionsare generally adjusted to the range of about 1.5 to about 12 (e.g., arange of 1.5 to 11) with the pH usually being adjusted in the preferredrange of about 2 to about 4 because the aqueous solutions during testinghave shown to be most stable at this pH range. Generally, the pH of theaqueous solutions containing the hydrolyzed silane-based compositions isadjusted based upon the R" group selected. The pH of the aqueoussolutions can be adjusted to the desired pH by the addition of a basicor acidic compound.

The aqueous solution containing the hydrolyzed silane-based compositioncan be affected by aging which can eventually result in a decrease inthe amount of strengthening improvement of the brittle oxide substrate.Interestingly, slight aging can, in certain circumstances, bebeneficial; for instance GPTMO. However, with further aging, there is aneventual decrease in properties. The shelf life of the aqueous solutionscontaining the hydrolyzed silane-based compositions is based on acomposition by composition basis. For instance, with respect to anaqueous solution wherein the hydrolyzed silane-based composition ishydrolyzed CETMO, a shelf life of at least 100 days is possible withoutany effect on the ability to substantially improve the strength of thebrittle oxide substrate.

The aqueous solution containing the hydrolyzed silane-based compositionis deposited or coated onto the substrate surface by spraying, dripping,dipping, painting, or any other techniques suited to the application ofliquids, vapors, or aerosols. Preferably, the aqueous solutioncontaining the hydrolyzed silane-based composition is applied as a sprayin an added or substituted spray step in the present commercialproduction and treatment of glass containers such as bottles, discussedbelow, using conventional spray equipment.

The coating of the present invention can be applied directly onto anysurface (e.g., internal, external, or portions thereof) of the brittleoxide substrate or can be applied to an exterior layer the compositionof which is different from that of the brittle oxide substrate. Forinstance, the coating of the present invention can be applied to a tin-,titanium-, silicon-, or other metal-oxide layer or mixtures of suchmaterials and still be effective in strengthening the brittle oxidesubstrate.

Typically, in the production of glass containers such as bottles, thebottles, which are on a conveyor line pass through 1) a hot end coatinghood wherein a layer of an inorganic tin is applied, such as tin oxide;2) an annealing lehr; and 3) a lubricant spray step. By using the methodof the present invention, the application of the aqueous solutioncontaining the silane-based solution preferably occurs after the glassbottles exit the annealing lehr and would be considered a cold-endcoating.

The aqueous solution containing the silane-based composition can beapplied at any temperature below the boiling point of the aqueoussolution, but generally is applied at or near room temperature.

Further, while the aqueous solution containing the silane-basedcomposition can be applied at any brittle oxide (e.g. bottle) surfacetemperature above the freezing point of the aqueous solution, a brittleoxide surface temperature from about 20° to about 200° C. is preferred,and a surface temperature from about 50° to about 60° C. is mostpreferred.

Once the brittle oxide substrates (e.g. glass bottles) are coated withthe aqueous solution containing the silane-based composition, the coatedbrittle oxide substrates enter a curing unit, such as a curing oven,wherein the surfaces of brittle oxide substrates usually obtain atemperature of at least about 230° C. Certainly, effective curing withsurface temperatures lower than 230° C. are possible with certainsilane-based coatings such as with BTMOE. Once this surface temperatureis obtained effective curing occurs. For instance, the surfacetemperature can be held at the at least about 230° C. for about 30seconds. The temperatures used during curing need to be high enough tocure the coated brittle oxide substrates without browning the coating.The temperature range for effective curing is based, in part, on the R"group selected. For instance, for hydrolyzed CETMO, generally,temperatures below about 200° C. provide marginal results andtemperatures above about 350° C. result in the charring of the coating.

The cure step in the method of the present invention can be effected bythe application of energy of any source at a magnitude sufficient toremove, e.g., water or other non-coating reaction products from thesurface of the treated brittle oxide substrate, provided that suchapplication is not deleterious to either the brittle oxide substrate orthe coating material. The curing step, being a combined function ofenergy and time, can include a low magnitude of energy for a relativelylong time, or the reverse, an application of a high magnitude of energylimited as noted hereinabove, for a relatively short period of time.Examples of such energy sources include microwave, infrared, ultraviolet(UV), irradiation or exposure to ambient or elevated temperatures, suchas in an electric or gas heating oven, at, above or below atmosphericpressure, or a combination of such conditions.

After exiting the curing step, a conventional lubricant spray step,mentioned above, can be used to add a polymer coating such aspolyethylene to the brittle oxide substrates for purposes of lubricity.The coatings of the present invention permit the adhesion of thelubricant to be at least as good as the adhesion of the lubricant to thehot end coating discussed above.

With the coatings of the present invention, it is possible to obtainsufficient lubricity in the brittle oxide substrate in order to avoidany lubricant spray step, especially with regard to bottlemanufacturing.

Strength, as described herein, refers to the maximum load a specimen canwithstand prior to catastrophic failure (and destruction of thearticle). There are numerous methods for measuring failure strengthdependent upon sample geometry and article application. These includebending strength, vertical load, burst pressure, concentric ringstrength, and impact testing.

The method of the present invention actually strengthens the brittleoxide substrate. As stated in the background, theoretically, all brittleoxide substrates, especially glass, are damaged in some way by minuteflaws or by the presence of small impurities. Since the brittle oxidesubstrates theoretically should have a much higher strength, one couldcharacterize the present invention as a method of restoring strength toa brittle oxide substrate since the method of the present invention isproviding a degree of strength to the brittle oxide substrate which iscloser to its theoretical strength.

One way of measuring the actual strength of the brittle oxide substratewith and without the coating of the aqueous solution containing ahydrolyzed silane-based composition is by a concentric ring strengthtest as described in the Journal of Strain Analysis, Vol. 19, No. 3(1984) and the Journal of Non-Crystalline Solids, 38 & 39, pp. 419-424(1980), which is a test commonly recognized by those skilled in the art.

Another way of measuring the strength is by a burst pressure strengthtest as described in ASTM Test C-147 using a ramp pressure tester(obtained from AGR, Intl. Literature), which is a test also commonlyrecognized by those skilled in the art.

A further way of measuring the strength is by an impact strength test asdescribed in the instructions which are provided with the AGR ImpactTester. This test is industry recognized and is accomplished with theuse of an AGR impact tester unit obtained from AGR, Int'l., Butler, Pa.The strength test is commonly recognized by those skilled in the art aswell.

As noted, the application of the aqueous solution containing thehydrolyzed silane-based composition of the present inventionsubstantially improves the strength of a brittle oxide substrate. Thesubstantial strength improvement is demonstrated by the concentric ringstrength, burst pressure strength, or impact strength improving at leastabout 10%. Preferably the strength improvement is at least 20%.

Those skilled in the art will recognize that by increasing the strengthof a brittle oxide substrate or article, e.g., glass, a lesser amount ofoxide substrate is needed to form an article of substantially equivalentstrength and general mechanical performance. Thus, in the specific caseof a glass container (e.g., the strength of the uncoated glass containerin the range of 10 to 600 psi as measured by burst pressure testing)such as a bottle, for instance, the bottle can be lighter in weight thanits untreated counterpart. Furthermore, increasing the strength leads toless failures of the product (e.g., less breakage) during commercialuse.

It is theorized that the polymerized cross-linked siloxane linkageoccurs within the coating, as well as between the coating and thebrittle oxide substrate surface. The coating, after bonding to thesurface, can act to heal cracks in the surfaces by forming an Si--O--Sinetwork across the flaw surfaces. The formation of the siloxane bonds inthe region of the flaws acts to provide an increase in the breakingstress of the article.

For a coating to actually restore or increase strength to a sample whichhas previously been damaged, the effect of stress-concentrating flaws onthe tension-bearing surface must be minimized. This requires a partialor complete healing of the flaws in the tension-bearing surface. For aglass container being pressure-tested, the surface experiencing tensionis predominantly the external surface of the bottle since the wallsactually bow outward as pressure is increased. In general, that externalsurface will be the one which develops a convex curvature duringloading.

It is possible, however, to increase the load required for impactfailure of a sample without necessarily restoring strength to thesubstrate. This technique makes use of a coating on the surface beingimpacted, rather than the side experiencing the tensile strength.(Impact generally induces a tensile stress in the interior surface of acontainer.) The mechanism in this case relies upon the ability of thecoating to absorb the energy of the impact such that the energy is nottransmitted to the substrate in the form of a flexural stress. Themeasured impact load for failure will be increased, but the flexuralstrength of the object will not have changed.

Commercially produced glass containers (e.g., a wall thickness in therange of 0.1 to 6 mm) are typically coated with a metal-oxide filmshortly after fabrication, using chemical vapor deposition; this isreferred to as a hot-end coating (HEC). Generally, this coating will betin oxide, but can be titanium or other metal oxide, and can have otheringredients to enhance physical properties, e.g., electricalconductivity. This coating is typically about 50 to 125 Å thick. Thepresent invention restores or increases the strength of damaged glass,whether or not a previously deposited HEC exists on the surface.

With respect to labelability of the brittle oxide substrate, it is to beunderstood that certain cured hydrolyzed silane-based coatings of thepresent invention do not interfere with this labelability as discussedpreviously. Labelability is measured by the following label peel test.

A paper label with four corners and having an area of about 6 squareinches is used. The label is weighed prior to the application of anon-casein type adhesive identified as 4242 available from NationalStarch. About 0.6 grams of the non-casein type adhesive is applied tothe back of the label (opposite side) and spread on the label by rollingwith a 5 mm glass rod or similarly shaped object to uniformly spread theadhesive on the label. The label is pressed on a surface of a brittleoxide substrate and allowed to dry for a minimum of two hours at roomtemperature. The label is peeled by hand at every corner until a portionof the label tears from every corner of the substrate. A coating isconsidered to have acceptable labelability for purposes of the presentinvention if greater than about 50% by weight of the label remains onthe surface of the brittle oxide substrate.

Preferably, the labelability (based on the % by weight of the labelremaining on the surface of the brittle oxide substrate) of the coatedbrittle oxide substrates of the present invention is greater than about60%, most preferably greater than about 70% by weight.

The substantially improved strength from the cured coating on thebrittle oxide substrates can also exhibit a maintained resistance to thedetrimental effects of humidity. In fact, a humidity resistance testprovides an acceptable way of determining how well the coatings of thepresent invention allow a coated brittle oxide surface to retain theimproved or restored strength. The excellent and maintained resistanceto humidity which can be exhibited by the silane-based coatings of thepresent invention is generally dependent upon the R" group. One way todetermine the effect of humidity on the coatings of the presentinvention is to compare the strength of coated brittle oxide substratewhen the cured coating on the substrate is less than 3 hours old atrelative humidity which generally is approximately 40%, with thestrength of the same coated brittle oxide substrate subjected to a 90%humidity for a period of 30 days. In such a test, the humidityresistance of the cured coatings of the present invention applied to thebrittle oxide substrates has only about a 50%, preferably only about20-30%, most preferably 0-10%, change in strength which is excellent,especially for purposes of glass bottles subjected to high humidityenvironments such as in the southern United States.

Interestingly, not all of the hydrolyzed silane-based coatings provideexcellent humidity resistance once coated onto a brittle oxidesubstrate. For instance, and as a comparison, when a hydrolyzedsilane-based composition, wherein R" is vinyl or methyl, is coated ontoa brittle oxide substrate and cured, the strength of the substratesubstantially improves, (e.g., 110% improvement (concentric ring test)when R" is vinyl and 200% improvement (concentric ring test) when R" ismethyl) and excellent humidity resistance is obtained (e.g., 0% loss(100% strength maintained) when R" is vinyl and 0% loss (100% strengthmaintained) when R" is methyl); however, when a hydrolyzed silane-basedcomposition, wherein R" is 2-(3,4 epoxycyclohexyl)ethyl orglycidoxypropyl, is coated onto a brittle oxide substrate and cured,while the strength of the coated substrate substantially improves (e.g.,200% improvement (concentric ring test) when R" is 2-(3,4epoxycyclohexyl)ethyl and 200% improvement (concentric ring test) whenR" is glycidoxypropyl), only fair humidity resistance is obtained (e.g.,40-50% loss (50-60% strength maintained) when R" is 2-(3,4epoxycyclohexyl)ethyl and 90-100% loss (0-10% strength maintained) whenR" is glycidoxypropyl).

This is all the more interesting when the labelability of these coatingsare compared:

    ______________________________________                                        R"                 Labelability                                               ______________________________________                                        methyl             0%                                                         vinyl              0-10%                                                      2(3,4 epoxycyclohexyl)ethyl                                                                      >60%                                                       glycidoxypropyl    >60%                                                       ______________________________________                                    

However, as stated earlier, the coating applied to the brittle oxidesubstrate can be a mixture of one or more hydrolyzed silane-basedcompositions.

Thus, the present inventors have discovered mixtures which providesubstantially improved strength along with excellent labelability andhumidity resistance. A mixture of a hydrolyzed silane-based compositionwherein R" is methyl and 2-(3,4 epoxycyclohexyl)ethyl is one excellentexample. It is all the more remarkable that when such a mixture is made,none of the individual components in the mixture detract from any of thedesired properties. For instance, the presence of MTMO does not detractfrom the labelability properties.

The aqueous solutions containing the hydrolyzed silane-basedcompositions of the present invention are non-flammable especially inview of the fact that there is a substantial absence of organic solventsin the aqueous solution.

When coating brittle oxide substrates, especially glass containers, itis preferred that the hydrolyzed silane-based composition is not visibleon the container. The silane coating should not discolor or becometextured upon curing. The hydrolyzed silane-based compositions of thepresent invention meet this criteria. It is noted that in somecommercial applications, a coating which is diffused (some haze orfresco) is desired. The coatings of the present invention are alsocapable of this diffused appearance by using an application temperature(e.g. brittle oxide substrate surface temperature) of from about 80° C.to about 100° C.

Further, color dyes can be added to the aqueous solution in order tomake colored coatings. Examples of suitable dyes include Celestine blue,Bismark brown, and Eriochrome black.

Further, dyes can be used in the aqueous solution for indicating thedegree of cure and spray coverage. In addition, other components can beincluded in the aqueous solution, such as UV blockers and fluorescingagents. Including a fluorescing agent will permit the coated brittleoxide substrates to have a "glow-in-the-dark" property.

The coatings of the present invention also advantageously have theability to hide visible scuff damage to a substrate surface. This isparticularly desirable in the refillable bottle industry wherein bottleseventually develop a whitened track around the bottle from numerouscycles through a filling line.

The present invention will be further clarified by the followingexamples, which are intended to be purely exemplary of the presentinvention.

EXAMPLE 1

In this example, soda-lime glass rods were indented with a Vickersdiamond to produce approximately 50-micro-meter (um) flaws in thesurface. These rod samples were tested to failure in bending, and hadaverage strengths of 56 MPa. Samples with identical flaws werespray-coated with a solution of 10 percent by weight (wt. %) of vinyltrimethoxysilane (VTMO) in water. The solution contained enough sulfuricacid to adjust the pH to between 3.0 and 3.4. The samples werethereafter heat-treated for 15 minutes (min.) at 200° C., and tested inbending. The average strength of these samples increased from 56 MPa to90 MPa.

EXAMPLE 2

Example 2 is a modification of Example 1. In this example, the sampleswere again indented rods, and the solution was 10 wt. % VTMO, acidifiedas set forth in Example 1. This solution also contained 0.75 wt. % ofthe nonionic surfactant Triton X-102. After curing, the indented samplesincreased in strength from 56 MPa to 93 MPa.

EXAMPLE 3

Example 3 is identical to Example 1, with the exception that the silaneused was methyltrimethoxysilane (MTMO). The control samples had anaverage strength of 62 MPa. Upon coating and curing, the bend strengthwas increased to 96 MPa.

EXAMPLE 4

Example 4 is a duplication of Example 2, using MTMO. The average controlstrengths were again 62 MPa, but the strengthened samples averaged 103MPa.

EXAMPLES 5 and 6

Examples 5 and 6 are duplicates of Examples 1 and 2, respectively, withthe exception that the silane used wasmethacryloxypropyltrimethoxysilane (MPTMO). For these samples, theaverage control strength was 60 MPa.

Once coated, these samples were thermally cured as described above, butwere also subjected to an additional UV irradiation in order to enhancethe curing. The strengthened samples for Example 5 attained an averagestrength of 126 MPa, while those for Example 6 reached 124 MPa.

EXAMPLE 7

This example illustrates the treatment of flat-glass samples which wereindented with a Vickers diamond to form a controlled flaw. Samples wereindented such that 90-um flaws were produced. These samples were coatedwith a silane solution consisting of three silanes in the same weightproportion. The overall silane concentration was 10 wt. % in water,while the amount of each silane was about 3.33 wt. %. The solutioncontained enough sulfuric acid to bring the pH to between 3.0 and 3.4. Anonionic surfactant, Triton X-102, was added in the amount of 0.75 wt. %in order to increase wetting. The 1:1:1 solution consisted ofglycidoxypropyltrimethoxysilane (GPTMO), 2-(3,4epoxycyclohexyl)ethyltrimethoxysilane (CETMO), and MTMO.

The control strengths were 45 MPa, while the samples treated with the1:1:1 solution were 160 MPa after a two-step cure consisting of a15-minute cure at 125° C., followed by a cure at 225° C. for 10 minutes,an increase in strength of about 3.5 times. Good labelability was alsofound for this mixture even though MTMO (generally exhibiting poorlabelability by itself) was present in the formulation.

EXAMPLE 8

The same control samples as described in Example 3 were strengthenedusing a 1:1 solution of GPTMO and CETMO, also in a 10 wt. % totalconcentration. The solution contained enough sulfuric acid to bring thepH to between 3.0 and 3.4. These samples underwent the same heattreatment described in Example 3. The strength of the treated sampleswas increased to 118 MPa from the starting strength of 45 MPa, for anincrease in strength of about 2.6 times.

EXAMPLE 9

The same flaws described in Example 3 were applied to the sidewalls ofamber bottles. The average burst pressure of these flawed containers was1.9 MPa. The flawed bottles were then silane-treated, using a 10 wt. %solution of CETMO and the same cure procedure described in Example 3.The average burst strength of the treated control-flawed samples wasincreased to 3.2 MPa, an increase of 68% over the flawed controlsamples.

EXAMPLE 10

Standard 12-ounce (oz.) beer bottles were indented as described inExamples 3 and 9. The average burst pressure of these flawed containerswas 1.9 MPa. Samples were coated and cured with the 1:1:1 solution asdescribed in Example 7. The average burst strength was increased fromthe control value of 1.9 MPa to 3.5 MPa for the treated samples.

EXAMPLE 11.

Lightweight 12-oz. bottles were indented as set forth above, and coatedwith the 10% CETMO solution described in Example 9. The average burstpressure for the indented controls was 1.5 MPa. Upon spray-coating, andsubsequent curing as set forth in Example 3, the average burst pressureof the bottles was increased to 2.6 MPa.

EXAMPLE 12

Lightweight 12-oz. bottles were coated in the as received state with a10 wt. % solution of CETMO. The burst strength of the control sampleswas 1.6 MPa. The coated and cured samples had an average burst strengthof 3.0 MPa.

EXAMPLES 13 THROUGH 16

In these examples, soda-lime flat-glass specimens were indented with aVickers diamond tip to produce the 50-um flaws on the surface asdescribed in Example 1. These samples were tested with a concentric-ringfixture. The mean strength of these uncoated samples was 69 MPa.

EXAMPLE 13

A suspension of MPTMO was prepared by adding the silane to wateracidified to a pH of 2.5 with a suitable acid, e.g., H₂ SO₄, to give a10 wt. % mixture. 0.5 wt. % Triton X-102 was added, and the compositionaged for 24 hours at room temperature. The condensing oligomersphase-separated at room temperature after 24 hours, forming asuspension. This suspension was applied by drip-coating over the flawregion and heat-treating for 15 min. at 125° C., followed by an UV cure.The mean flat-glass strengths were 223 MPa.

EXAMPLE 14

A 10 wt. % suspension of methacryloxypropylmethyldiethoxy-silane(MPMDEO) was prepared using the same procedure as described in Example10, but using the surfactant at a 1 wt. % level. The suspension wasdrip-coated on flat glass and the coating was cured for 15 min. at 125°C. followed by a cure at 225° C. for 10 min. The treated flat-glassspecimens had mean strengths of 143 MPa.

EXAMPLE 15

A 10 wt. % suspension containing a 1:1 wt. mixture ofdimethyltetramethoxydisiloxane and MPMDEO was prepared as described inExample 10, except that acetic acid was used to adjust the pH to 3.5,and no surfactant was added. The sample received a dual cure asdescribed in Example 14. The treated flat-glass specimens had meanstrengths of 193 MPa.

EXAMPLE 16

A 10 wt. % suspension containing a 1:1 wt. mixture ofdi-tert.-butoxydiacetoxysilane (DBDAS) and MPMDEO was prepared asdescribed in Example 14, except that H₂ SO₄ was used to adjust the pH to3.5, and 0.025 wt. % Triton X-102 was added. The sample received a dualcure as described in Example 12. The treated flat-glass specimens hadmean strengths of 152 MPa.

EXAMPLE 17

In this example, flat soda-lime glass specimens were indented with aVickers diamond to produce approximately 50-um flaws. The samples weretested with a concentric-ring fixture, and had average strengths of 69MPa. A solution of 10 wt. % of DBDAS in water was adjusted with aceticacid to a pH of 3.5. The solution was drip-coated onto a flat glassspecimen, and the article thermally cured for 15 min. at 125° C. Thecured specimens had a mean strength of 133 MPa.

EXAMPLE 18

Flat-glass specimens were treated as in Example 17. The pH of a solutionof 10 wt. % GPTMO in water was adjusted with H₂ SO₄ to 3.5. The solutionwas stored at room temperature for two weeks, after which the flawedslides were drip-coated with the solution and cured first at 125° C. for15 min. and then at 225° C. for 10 min. The mean strength was 219 MPa.

EXAMPLE 19

Flat soda-lime-glass specimens were indented with a round diamond tip toproduce a readily visible impact flaw. The specimens had meanconcentric-ring strengths of 43 MPa.

The pH of an aqueous solution of 30 wt. % CETMO in water was adjustedwith H₂ SO₄ to 3.5. The solution was drip-coated onto the flawed slideand thermally cured at 125° C. for 15 min. and then at 225° C. for 10min. The mean strength was 61 MPa.

EXAMPLE 20

Soda-lime glass flat-glass specimens were indented with a Vickersdiamond to produce approximately 50-um flaws. These samples were testedwith a concentric-ring fixture, and had average strengths of 69 MPa. Asolution of 10 wt. % N-(3-triethoxysilylpropyl)-4-hydroxybutyramide(HBTEO) was prepared in water and allowed to stand for 30 days; the pHwas 9.5. The flawed slides were then drip-coated with the solution, anddual-cured at 125° C. for 15 min., followed by 225° C. for 10 min. Thetested mean strength after treatment was 266 MPa.

EXAMPLE 21

Soda-lime flat-glass specimens were indented with a Vickers diamond toproduce approximately 50-um flaws. These samples were tested with aconcentric-ring fixture, and had average strengths of 69 MPa.

Flat-glass specimens were dip-coated with undiluted MPTMO, then cured bypassing them three times through a UV curing apparatus at an energylevel of 5.3 Joules per square centimeter per pass. The mean strength ofspecimens so treated was increased to 104 MPa.

EXAMPLE 22

Soda-lime flat-glass specimens were indented as set forth in Example 21,and then coated with 150Å of pyrolytically deposited SnO₂. The sampleswere then annealed to remove residual stresses. Tin-oxide-coated controlsamples strengths of about 83 MPa.

The SnO2-coated specimens were then treated with a 10 wt. % solution ofMTMO as described in Examples 3 and 4, producing specimens withstrengths of 210 MPa.

EXAMPLE 23

Soda-lime flat-glass specimens were indented with a Vickers diamond toproduce approximately 50-um flaws. These samples were tested with aconcentric-ring fixture, and had average strengths of 69 MPa. A solutionof 10 wt. % of 3,3-dimethoxypropyltrimethoxysilane (DMPTMO) in water wasprepared, and the pH adjusted to 3.5. After standing for two hours atroom temperature, one portion of the solution was used to drip-coat theflawed slides. The slides were then cured at 125° C. for 15 min. andthen at 225° C. for 10 min. The mean strength for the treated slides was88 MPa. ¹ H nuclear-magnetic-resonance (NMR) analysis of the DMPTMOsolution showed only the --CH(OCH₃)₂ group of the silane triol as asignal at 4.41 (triplet) ppm.

Another portion of the same solution, after standing 192 hours at roomtemperature, was used to drip-coat different slides flawed identically,and then cured as above. The mean strength of these slides was 256 MPa.NMR analysis of this solution showed --CH(OH)(CH₃), --CH(OH)₂, and --CHOgroups of the silane triol in equilibrium with an approximate abundanceof 4:4:2 as signals at 4.55 (triplet), 4.90 (triplet) and 9.63 (singlet)ppm, respectively.

EXAMPLE 24

The present invention was tested at a bottling manufacturing facilitybased on the following procedure: 120 16-ounce glass beverage containerswere pressure tested prior to treatment using an AGR ramp pressuretester. The average burst pressure measured was 422 psi (2.9 MPa), andthe percentage of the bottles failing below 300 psi (2.1MPa) was 15%.The treatment process consisted of spraying a solution of the presentinvention (specifically, CETMO), thermally curing to achieve 230° C. orbetter, followed by a standard cold-end-coating application. 120containers having this treatment were burst-pressure tested in the samemanner as those described above, yielding an average burst pressure of490 psi (3.4 MPa) (increase of 16%) and a failure rate below 300 psi(2.1 MPa) of 6% (a decrease of 57%).

EXAMPLE 25

Vickers indented float glass was drip coated with an aqueous 10%solution of 3-ureidopropyltrimethoxysilane (UPTMO) having a pH of 3.4and 0.05% Triton X-102 surfactant. The samples were thereafter heattreated at 125° C. for 15 minutes followed by 225° C. for 10 minutes.The concentric ring strengths were

    ______________________________________                                        uncoated           9588 psi (66.1 MPa)                                        coated            25492 psi (176 MPa)                                         ______________________________________                                    

EXAMPLE 26

Example 25 was repeated with the exception that the silane was1,2-bis(trimethoxysilyl)ethane. The control samples had an averageconcentric ring strength of 11566 psi (79.8 MPa). After coating andcuring, the average concentric ring strength was 19728 psi (136 MPa).

EXAMPLE 27

Example 26 was again repeated with the exception that the heat treatmentconsisted of only heating at 125° C. for 15 minutes. The averagestrength went from 11566 psi (79.8 MPa) (uncoated) to 23799 psi (164MPa) after coating and curing.

EXAMPLE 28

Example 25 was repeated with the exception that the silane was1,2-bis(3-trimethoxysilylpropoxy)ethane. BTMOPE was made using thefollowing procedure.

Allyl bromide, 0.7 mole, was added dropwise over 1.5 hrs. to a stirredmixture of 0.33 mole of ethylene glycol, 1.25 moles of 50 % aqueoussodium hydroxide and 0.025 mole of tributylmethylammonium chloride. Themixture was heated at 80°-90° for 12 hours. The mixture was cooled to25° C. and the aqueous phase separated and was discarded. The organicphase was diluted with 5 volumes of ethyl ether, washed with saturatedsodium chloride solution and dried over sodium sulfate.1,2-bis(allyloxy)ethane, BAOE, was isolated by distillation underreduced pressure, b.p 89°-90° C. @ 50 torr.

A mixture of 0.075 mole of BAOE and 50 microliters of platinum divinylcomplex in xylene (Huls America, cat # PC072) was heated to 85° C.Trimethoxysilane, 0.160 mole, (Aldrich Chem. Co.) was added dropwise tothe stirred mixture over a 2 hour period under an inert atmosphere. Themixture was stirred at 85° C. for 2 hours then distilled under reducedpressure. BTMOPE was isolated as the fraction with a boiling point135°-136° C. at 0.25 torr. The concentric ring strengths of the sampleschanged from 10139 psi (69.9 MPa) (uncoated) to 29183 psi (201 MPa)after coating and curing.

EXAMPLE 29

Example 27 was repeated using the silane of Example 28. The strength ofthe coated and cured samples averaged 30153 psi (208.0 MPa) while thecontrols average 10139 psi (69.9 MPa).

EXAMPLE 30

0.5 wt. % Celestine Blue dye (CAS # 1562-90-9) was added to a 5%solution of CETMO that also contained 0.025% Triton X-102 surfactant.The solution was then spray applied onto 16-oz beverage containers using2.0 g of solution/bottle. The samples were then heat treated for 33seconds in an infrared oven set at 700° C. The coated bottles had auniform blue coating.

EXAMPLE 31

To a 10% CETMO solution containing 0.05% Triton X-102 surfactant wasadded 1 wt. % each of Uvinul MS-40 (obtained from BASF Corp.) andTinopal CBS-X (obtained from Ciba-Geigy Corp.). The solution was sprayapplied onto flat glass. The samples were heat treated using the methodof Example 25. The final coating thickness was 0.9 micrometers. Thesamples were measured for their UV transmission before and after coatingand curing. The results showed:

    ______________________________________                                                      % Transmission at λ                                      Sample          λ = 340 nm                                                                        λ = 380 nm                                  ______________________________________                                        Uncoated        89         90                                                 Coated and Cured                                                                               5         27                                                 ______________________________________                                    

EXAMPLE 32

A silane mixture was prepared as follows:

One gram of Nafion 50 perfluorinated acid resin, 2 grams (0.0085 mole)of GPTMO, and 2 grams (0.11 mole) of deionized water were added togetherin a plastic bottle at room temperature. After 15 minutes, 91.9 grams ofadditional water was then added along with 3 grams (0.017 mole) of MTEO(methyltriethoxysilane) and 0.1 gram of Tritron X-102 to give 100 totalgrams of solution.

This formulation (at 1 hour and 20 days old) was spray applied toone-minute-line-simulated 16-oz beverage bottles at a surfacetemperature of 55° C. (using an AGR line-simulator). The bottles werecured at an average surface temperature of 225° C. for 30 seconds. Thebottles exhibited burst pressure increases of 51 and 71% over theuntreated controls respectively.

The bottles then had a 0.6 gram label (having four corners) containing0.6 gram of adhesive applied to the surface. The adhesive was allowed toset up for 16 hours (overnight) at room temperature. The bottleexhibited a 75-80% retention (cohesive failure) of label when four (4)attempts to remove the label were made (i.e., the label was peeled byhand at every corner until a portion of the label teared off). Acomparable 1 hour old formulation of 5 grams MTEO and 0.1 gram of TritonX-102, applied in the same manner on the same type of bottles, exhibitedno retention of the label (adhesive failure).

EXAMPLE 33

Rectangular alumina bars were tested in 3-point bending to evaluate theability of the present invention to strengthen it. Half of the aluminasamples (n=6) were tested as controls using the Instron configured in a3-point bend arrangement. The other half of the samples werespray-coated with 10% by weight CETMO/0.025% by weight TritonX-102/0.025 % by weight RP-40 (obtained from T. H. Goldschmidt, Germany)formulation and thermally cured using the 2-step heat treatment protocol(15 minutes at 125° C. followed by 10 minutes at 225° C.). The controlsamples had an average failure strength of 23,300 psi, while the treatedsamples had an average strength of 28,200 psi. This represents anaverage increase of 21%.

In view of the results reported by Hashimoto et al. in U.S. Pat. No.4,891,241, with respect to their comparative examples 1, 2 and 3, givenat col. 25, lines 27 through 29, where they found no increase instrength when only silanes were used as a coating, the degree ofimprovement in strength afforded by the treatment of the examplesdescribing the present invention is quite surprising. As noted in thepresent specification, no additional treatment, such as described byHashimoto et al., is used, yet the improvement in strength of thetreated glass rises to two or more times that of the untreated controls,and the variability in observed strengthening is relatively small. Theimprovement afforded by the present invention is especially surprisingin view of the teaching of Hashimoto et al. at col. 5, lines 36 et seq.,where they note that the treatment of the substrate with siloxanes aloneis insufficient to produce strengthening, and that a polymeric overcoatis essential for the development of the strengths reported.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples to be considered as exemplary only, with a true scope andspirit of the invention being indicated by the following claims.

What is claimed:
 1. A composition useful for coating a brittle oxidesubstrate comprising a mixture of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane and vinyltrimethoxysilane.
 2. A composition usefulfor coating a brittle oxide substrate comprising a mixture of2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane andmethyltrimethoxysilane.
 3. A composition useful for coating g brittleoxide substrate comprising a mixture of3-glycidoxypropyltrimethoxysilane, 2-(3,4-epoxycyclohexly)ethyltrimethoxysilane, and methyltrimethoxysilane.
 4. A compositionuseful for coating g brittle oxide substrate comprising a mixture of3-glycidoxypropyltrimethoxysilane and 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane.
 5. An aqueous-based composition useful forcoating a brittle oxide substrate comprising an effective amount of3-ureidopropryltrimethoxysilane to improve or restore strength in saidbrittle oxide substrate and a non-ionic surfactant.
 6. An aqueous-basedcomposition useful for coating a brittle oxide substrate comprising aneffective amount of 1,2-bis(trimethoxysilyl)ethane to improve or restorestrength in said brittle oxide substrate, and a non-ionic surfactant. 7.A composition useful for coating brittle oxide substrates comprising1,2-bis(3-trimethoxysilypropoxy)ethane.
 8. A composition useful forcoating a brittle oxide substrate comprising a mixture of an effectiveamount of 3,3-dimethoxypropyltrimethoxysilane to improve or restorestrength and improve humidity resistance in a brittle oxide substrateand an effective amount of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilaneto improve or restore strength and labelability in said brittle oxidesubstrate.
 9. A composition useful for coating a brittle oxide substratecomprising a mixture of a) an effective amount of 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,3-glycidoxypropyltrimethoxysilane, or both, to improve or restorestrength and labelability to said brittle oxide substrate and b) aneffective amount of vinyltrimethoxysilane,3,3-dimethoxypropyltrimethoxysilane, methyltrimethoxysilane, or mixturesthereof, to improve or restore strength and humidity resistance in saidbrittle oxide substrate.
 10. The composition of claim 9, wherein saidmixture is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysiliane andvinyltrimethoxysilane.
 11. The composition of claim 9, wherein saidmixture is 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane andmethyltrimethoxysilane.
 12. The composition of claim 9, wherein saidmixture is 3-glycidoxypropyltrimethoxysilane and vinyltrimethoxysilane.13. The composition of claim 9, wherein said mixture is3-glycidoxypropyltrimethoxysilane and methyltrimethoxysilane.